For a realization of flexible and electronic components based on organic semiconducting elements it is necessary to develop capable and robust organic transistors. A promising approach is provided by vertical organic field effect transistors (VOFETs).
A VOFET (as field effect transistors in general) is formed with three electrodes, namely a gate electrode, a source electrode and a drain electrode. In a VOFET, the source electrode and the drain electrode are connected with each other by an organic semiconductor. The gate electrode is separated from the source electrode and the drain electrode by an insulator. The elements of the VOFET are formed as a stack on a substrate, wherein the stack has one of the following sequences of layers: substrate/gate electrode/insulator/source electrode/drain electrode or substrate/drain electrode/source electrode/insulator/gate electrode. The organic semiconductor is always arranged between the source electrode and the drain electrode. Additionally, it can be arranged between the insulator and the source electrode. Two methods are known for producing a VOFET: self-organization of the materials and technical structuring, for example with a shadow mask.
The document WO 2010/113163 A1 discloses a vertical organic field effect transistor and a method for producing the same. The transistor comprises a patterned electrode structure which is enclosed between a dielectric layer and an active element. The active element is either an organic semiconductor or an amorphous semiconductor. The electrode structure is patterned by using a block copolymer material as a patterning mask. Hereby, the thickness of the patterned layer and lateral feature size can be selected.
A method for forming an organic device having a patterned conductive layer is disclosed in document WO 2011/139774. The method comprises the steps of depositing an organic layer on a substrate and coating the organic layer with a photoresist solution to form a photo-patternable layer. The photoresist solution includes a fluorinated photoresist material and a fluorinated solvent. Selected portions of the photo-patternable layer are radiated to form a pattern. A conductive layer is coated over the organic layer. A portion of the conductive layer is removed to form a patterned conductive layer.
K. Nakamura et al., Applied Physics Letters Vol. 89, page 103525 (2006) discloses an organic light emitting transistor. A gate electrode is arranged on a substrate and covered by a gate insulating layer. A semiconducting layer is coated on the gate insulating layer. A source electrode, an insulating layer, and a hole transporting layer are arranged on the semiconducting layer. Further, the transistor comprises an emitting layer and a drain electrode.
There is a need to provide a transistor design which allows high current densities in the device and which can be produced in an easy and controllable manner.